Simulating effects of fire on northern Rocky Mountain landscapes with the ecological process model FIRE-BGC

A mechanistic, biogeochemical succession model, FIRE-BGC, was used to investigate the role of fire on long-term landscape dynamics in northern Rocky Mountain coniferous forests of Glacier National Park, Montana, USA. FIRE-BGC is an individual-tree model-created by merging the gap-phase process-based model FIRESUM with the mechanistic ecosystem biogeochemical model FOREST-BGC-that has mixed spatial and temporal resolution in its simulation architecture. Ecological processes that act at a landscape level, such as fire and seed dispersal, are simulated annually from stand and topographic information. Stand-level processes, such as tree establishment, growth and mortality, organic matter accumulation and decomposition, and undergrowth plant dynamics are simulated both daily and annually. Tree growth is mechanistically modeled based on the ecosystem process approach of FOREST-BGC where carbon is fixed daily by forest canopy photosynthesis at the stand level. Carbon allocated to the tree stem at the end of the year generates the corresponding diameter and height growth. The model also explicitly simulates fire behavior and effects on landscape characteristics. We simulated the effects of fire on ecosystem characteristics of net primary productivity, evapotranspiration, standing crop biomass, nitrogen cycling and leaf area index over 200 years for the 50,000-ha McDonald Drainage in Glacier National Park. Results show increases in net primary productivity and available nitrogen when fires are included in the simulation. Standing crop biomass and evapotranspiration decrease under a fire regime. Shade-intolerant species dominate the landscape when fires are excluded. Model tree increment predictions compared well with field data.     

Chloramphenicol 3. Clinical pharmacology of systemic use in the horse

The use of chloramphenicol in the horse is now prohibited as horses are classified as food-producing animals. However, chloramphenicol has until recently been widely available for oral, intramuscular or intravenous administration. A critical appraisal of the published literature on the use of chloramphenicol in the horse clearly demonstrates that there are sound pharmacokinetic and microbiological reasons for concluding that chloramphenicol is not an appropriate antibiotic for systemic use. The short half-life of chloramphenicol in the horse, together with the broad range of minimum inhibitory concentrations of target pathogens, preclude the use of practical dosage regimens. It can be concluded that the withdrawal of chloramphenicol will have no adverse effects on chemotherapy in the horse.     

Decreasing photosynthesis at different spatial scales during the late growing season on a boreal cutover

The relationship between photosynthesis and accumulated cold degree days (CDD) over the late growing season was examined at the shoot, ecosystem and landscape scales in a boreal cutover in eastern Canada predominated by black spruce (Picea mariana Mill. BSP), lowbush blueberry (Vaccinium angustifolium Ait.) and sheep laurel (Kalmia angustifolia L.). We calculated CDD as the sum of minimum daily temperatures below a 5 degrees C threshold. Light-saturated photosynthesis at the shoot level (A(max)) of black spruce and V. angustifolium decreased steadily with increasing CDD once temperatures below the CDD threshold value became frequent in mid-September, whereas K. angustifolia showed a more irregular pattern. Tissue acclimation played an important role in the decrease in A(max) as the season progressed, but only V. angustifolium showed decreasing foliar nitrogen concentrations. Based on eddy covariance flux tower data, maximum daily gross primary productivity (GPP(max)-tower) at the ecosystem level was more strongly related to CDD (r(2) = 0.59) than was maximum daily net ecosystem exchange (r(2) = 0.32). The GPP(max) was likely influenced by both tissue acclimation and the direct effects of changing temperatures and irradiances on physiological rates. Mean daily GPP, calculated for consecutive 8-day periods for a 25 km(2) area around the tower by the MODIS MOD17A2 Collection 4 satellite algorithm (GPP- MODIS), decreased more rapidly with increasing CDD than did GPP(max)-tower. Although GPP-MODIS was closely correlated with mean daily GPP from the tower (GPP(daily)-tower, r(2) = 0.95) over the late growing season, the former was about twice as high. Although MODIS estimates of air temperature closely tracked the ground data, the maximum light-use efficiency parameter used by the MODIS algorithm was much higher than that indicated by the tower measurements. There was a 3% decline in GPP(max)-tower with an increase of 10 CDD, corresponding to the percent decline in branch-level A(max) of black spruce and V. angustifolium.     

The effects of aggregating sub-grid land surface variation on large-scale estimates of net primary production

The use of large grid cell databases (1/2° to 5°) to drive nonlinear ecosystem process models may create an incompatibility of scales which can often lead to biased outputs. Global simulations of net primary production (NPP) often assume that bias due to averaging of sub-grid variations in climate, topography, soils, and vegetation is minimal, yet the magnitude and behavior of this bias on estimates of NPP are largely unknown. The effects of averaging sub-grid land surface variations on NPP estimates were evaluated by simulating a 1° × 1° land surface area as represented by four successive levels of landscape complexity, ranging from a single computation to 8,456 computations of NPP for the study area. Averaging sub-grid cell landscape variations typical of the northern US Rocky Mountains can result in overestimates of NPP as large as 30 %. Aggregating climate within the 1° cell contributed up to 50 % of the bias to NPP estimates, while aggregating topography, soils, and vegetation was of secondary importance. Careful partitioning of complex landscapes can efficiently reduce the magnitude of this overestimation.     

Antagonism of detomidine with tolazoline in isoflurane-anaesthetised ponies

The effects of tolazoline (4.0 mg/kg iv) antagonism of detomidine (0.02 mg/kg iv) were evaluated in isoflurane-anaesthetised, ventilated ponies. Each of 6 ponies received both tolazoline and saline treatment during separate anaesthetic episodes only (no surgery was performed). Detomidine administration produced an increase in blood pressure, decrease in heart rate and decrease in P_aO₂ Tolazoline treatment transiently increased heart rate while blood pressure returned to baseline after both treatments. Arterial oxygenation decreased further after tolazoline treatment while oxgenation recovered towards baseline with saline treatment. No other cardiopulmonary effects were detected. Recovery from anaesthesia tended to be more rapid when detomidine was antagonized. The potential benefit of antagonizing detomidine-induced bradycardia with tolazoline, during isoflurane anaesthesia should be weighed against the potential to produce a decrease in arterial oxygenation. The mechanism for this effect is not clear.     

Water/nutrient interactions affecting the productivity of stands of Pinus radiata

The accumulation of above-ground biomass and the seasonal patterns of leaf-area development, foliar nutrient concentrations and tree and soil water-status have been measured for fertilised, irrigated, and control stands of Pinus radiata D. Don growing on a low-productivity site, average annual precipitation of 790 mm, near Canberra in southeastern Australia. In the second growing-season after treatments commenced, projected leaf-area index reached peak values of 7 on the irrigated/fertilised stands compared with approximately 5 on the other stands. Average canopy nitrogen concentration (dry-weight basis) varied across the treatments from 9 to 17 mg g⁻¹. Measurements of soil and tree water-status over a 2-year period indicated that stands which were not irrigated experienced summer droughts of up to 4 months duration.

Annual volume production measured over the 2-year period ranged from 17 to 45 m³ ha⁻¹. The extent to which this variation could be attributed to differences in leaf area, rats of photosynthesis, duration of the period of positive net photosynthesis, and hence growth, was analysed in terms of a process-based model of stand growth dependent on climate and soil water-balance.

Annual canopy net photosynthesis simulated by the model ranged from 18 t carbon ha⁻¹ for the control stand to 38 t ha⁻¹ for the irrigated/fertilised stands. Simulations indicated that 67% of this difference could be attributed to the role of irrigation in extending the period of active growth. The additional leaf area carried by the irrigated/fertilised stands contributed a further 23%, while differences in rates of photosynthesis, related to nitrogen nutrition, explained the remaining 10%.     

Signaling of cell fate decisions by CLAVATA3 in Arabidopsis shoot meristems

In higher plants, organogenesis occurs continuously from self-renewing apical meristems. Arabidopsis thaliana plants with loss-of-function mutations in the CLAVATA (CLV1, 2, and 3) genes have enlarged meristems and generate extra floral organs. Genetic analysis indicates that CLV1, which encodes a receptor kinase, acts with CLV3 to control the balance between meristem cell proliferation and differentiation. CLV3 encodes a small, predicted extracellular protein. CLV3 acts nonautonomously in meristems and is expressed at the meristem surface overlying the CLV1 domain. These proteins may act as a ligand-receptor pair in a signal transduction pathway, coordinating growth between adjacent meristematic regions.